Steel tops Forth tolls

Cairnhill Structures has recently completed the erection of a new steel canopy over the eight toll booths serving the Forth Road Bridge in Scotland.

The canopy is 41.5m long x 17.5m wide and is supported on eight steel 500mm x 300mm x 16 RHS columns. The structure is triangular in cross section and was constructed with 80t of steelwork.

Inside the canopy there is a hollow area containing a maintenance walkway and feature coloured lighting to illuminate the structure through its Expanded aluminium soffit and skewed wall cladding.

The steel consists of angle section rafters and internals supported on a grillage comprising 610mm x 305mm x 149mm UB primary and 610mm x 225mm x 101mm UB secondary beams.

Jack Sanderson, Cairnhill’s Managing Director said the project presented a number of challenges, not least the fact that the bridge couldn’t be closed during the four-month steel erection programme.

“Traffic management was in place and we were allowed to close only three booths at any one time,” Mr Sanderson said. “All steel brought on to site had to be erected immediately as nothing was allowed to be left stockpiled on the bridge,” he added.

Strong winds are not uncommon along the Forth and consequently the canopy was designed with a north facing sloping top to deflect the wind.

All canopy steelwork is galvanised to protect the structure from wind-borne salt which causes rust. And, as Mr Sanderson pointed out, “This means it won’t have to be continually repainted, unlike the bridge.”